In this modified version of the Tarod Spread Generator by Haley Halcyon, a code of 7 integers from 1 to 20 (i.e. 20-sided die rolls) separated by spaces is used to pick among 73'920 possible combinations of tarot readings. See the original Codepen for more background.
To the three cards, you can assign the meanings of “past/present/future”; “what you want/what the other party wants/where you are headed”, “the conscious/the subconcious/the world”, or other groups of three. There aren’t many rules at all in tarot reading; the cards simply serve as inspiration.
Tarot card images are from Wikimedia Commons.